CSC151 2007S, Class 51: Objects Lab

Admin:
* Are there questions on exam 3?
* EC for following the Ultimate Team to Decorah this weekend to 
  watch what happens when an upstart school goes up against a 
  national champion.
* EC for baseball tomorrow against the block plan place in Iowa.
* EC for concert at 11 a.m. in Herrick tomorrow.
* EC for orchestra concert on Friday.
* EC for inventing a time machine and going back to support past
  events.  NOT.
* EC for Savarese's reading tomorrow.

Overview:
* Review of reading.
* Lab.

/Review/
* (let (...)
  (lambda (...)
     ...))
  *Builds an "inpenetrable boundary" (spelling is determined by consensus,
anyway).
  * So that only the lambda can access the variables specified in the let
* We "send messages" to objects, and the objects react to the messages
  by using or changing "what's inside"
* (let (...)
  (lambda (message . params)
    (cond ((eq? message 'FOO) ...)
          ((eq? message 'BAR) ...)
          (else (error "...")))))
     ...))

* To build multiple objects, we write lambda let lambda (with many more parens)

* If we want to save object info, we need to use files